What Is a Corymb? A Flat Topped Flower Cluster
A corymb is a flower cluster where the outer flower stalks are longer than the inner ones. All the blooms end up at about the same height in a flat or domed top.
The short answer
Master Gardeners of Northern Virginia note corymb stalks rise from different levels on the main axis. The lower outer stalks are longer, so the flowers sit level. Iowa State notes corymbs bloom from the outside in. NC State calls the corymb a flat topped raceme, one of five indeterminate types.
How do you identify a corymb?
Follow each flower stalk back to the main stem. MGNV notes the stalks attach at different levels plus may be alternate or opposite.
| Cluster | Where stalks start | Opens first |
|---|---|---|
| Corymb | Different levels | Outer flowers |
| Umbel | One point at the top | Varies |
| Cyme | Branches below a center flower | Center flower |
| Raceme | Along one long stem | Bottom flowers |
Source: NC State plus Iowa State Extension.
How is a corymb different from an umbel?
NC State notes an umbel looks similar, but its stalks all arise from one point at the top of the axis. A corymb’s stalks rise from points along the axis.
Which plants have corymbs?
MGNV names northern highbush blueberry as a simple corymb. Chokeberry, some hawthorns plus mountain laurel bear compound corymbs.
How to: step by step
- Locate a flat topped flower cluster.
- Trace each stalk to the main stem.
- Check whether stalks attach at different points.
- Note longer stalks on the outside.
- Contrast with an umbel.
- See which flowers open first.
Troubleshooting
Stalks attach at different points: corymb.
Stalks meet at one point: umbel.
Center flower opens first: cyme. MGNV notes wild hydrangea has cymose corymbs that do this too.
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Sources
- Corymb (glossary), Master Gardeners of Northern Virginia
- Plant identification terminology: an illustrated glossary, Purdue Extension Master Gardener Program
- Glossary of garden terms, Iowa State University Extension and Outreach
- Extension Gardener Handbook, chapter 3: botany, NC State Extension
FAQ
Does blueberry have corymbs?
MGNV notes northern highbush blueberry has simple corymbs with unbranched stalks. Its Latin name, Vaccinium corymbosum, points to the cluster.
Which way does a corymb bloom?
Iowa State notes a corymb blooms from the outside in. That makes it an indeterminate cluster.
What is a compound corymb?
MGNV notes a compound corymb has branched stalks that form smaller corymbs. Chokeberry plus mountain laurel are examples.
Why do some flower clusters look flat?
MGNV notes the lower outer stalks are longer than the inner upper ones, so all the flowers rise to about the same height.
What does corymbose mean?
MGNV notes clusters arranged in the form of a corymb are called corymbose. Those that only look like one are corymbiform.
